Constant tension ball screw feed design

ABSTRACT

The invention herein is directed to a constant tension arrangement for a lead or ball screw drive for the purpose of preventing compressive forces from acting on an elongated ball screw or lead screw member to deform the same. The constant tension arrangement is provided by means of a bearing mounting in which thrust bearings are positioned on the ends of the screw member in such a manner that axial displacement in the direction of the support for the screw member is permitted. With this arrangement, and for either direction of motion of the driven nut thereon, any loading will effect a constant tension force on the ball or lead screw member opposite that of the loading permitting the remainder of the screw member to move axially and prevent compressive loading of the same.

United States atent [1 1 Cannon et al.

[45] Feb. 19, M74

[ CONSTANT TENSION BALL SCREW FEED DESIGN [73] Assignee: said Cannon, bysaid Pehoslri [22] Filed: Aug. 31, 1972 [21] Appl. No.: 285,531

Primary Examiner-Benjamin W. Wyche Assistant Examiner-Wesley S. Ratliff,Jr.

Attorney, Agent, or Firm-Schroeder, Siegfried, Ryan and Vidas [5 7]ABSTRACT The invention herein is directed to a constant tensionarrangement for a lead or ball screw drive for the pur pose ofpreventing compressive forces from acting on an elongated ball screw orlead screw member to deform the same. The constant tension arrangementis provided by means of a bearing mounting in which thrust bearings arepositioned on the ends of the screw member in such a manner that axialdisplacement in the direction of the support for the screw member ispermitted. With this arrangement, and for either direction of motion ofthe driven nut thereon, any loading will effect a constant tension forceon the ball or lead screw member opposite that of the loading permittingthe remainder of the screw member to move axially and preventcompressive loading of the same.

llll Claims, 5 Drawing Figures CONSTANT TlENSllON lBAlLL SCREW FEEDDESIGN Our invention relates to a ball screw or lead screw feed designand more particularly to an improved bearing construction for mountingthe lead or ball screw to provide for the application of constanttension on the same for either direction of motion and loading.

In the past, load bearing members such as lead screws have beenprestressed by means of external means, such as by applying a separatehydraulic force thereto, for the purpose of damping vibrations andflutter and increasing precision of operation. Further, load bearinglead screws of long lengths required larger sized screws to withstandthe loading.

The present invention is directed to an arrangement by means of whichthe mounting of the lead screw itself through suitable bearings and thearrangement of the same brings about an application of tension to thelead screw under load for either direction of movement to minimizevibrations and to prevent translational dis placement of the same. Thisis particularly true when the lead screw or ball screws are of increasedlength and under normal construction would be placed in compression withloading due to the drive of the same. This improved lead screw mountingarrangement permits a size reduction from that of the conventionalmounting for the same load requirements.

It is therefore the principal object of this invention to provide animproved lead or ball screw feed design and mounting arrangement inwhich the screw member is placed under constant tension for all loadingsand directions of motions.

Another object of this invention is to provide a sim plified structurein the form of the mounting of the lead screw through mechanicaljournaling means to insure the application of a tension force thereonfor all directions of motion.

A further object of this invention is to provide a lead screw mountingarrangement that permits a reduction in the cost of the lead screwbecause of size reduction.

These and other objects of this invention will become apparent from areading of the attached description together with the drawings wherein:

H0. 1 is a front elevation view of a drilling apparatus showing theapplication of the invention to lead or ball screws for driving thedrilling head;

FIG. 2 is a sectional view taken along the lines 22 orrro. 1;

FIG. 3 is a sectional view of FIG. 1 taken along the lines 3-3 thereinshowing the lead screw and its journal bearing mounting;

FIG. t is a sectional view taken along the lines 4-d of FIG. 3; and

HO. 5 is a sectional view of FIG. 3 taken along the lines 5-5 therein.

Our invention in a ball screw or lead screw feed design is shown in thedrawings in connection with a drilling rig or structure, the details ofwhich are omitted for simplicity. Thus in FIG. 1, the drill rig which isshown in front elevation is comprised of a base frame having a suitabletrack or motive drive structure 112 be neath the same with appropriateengines and power supplies (not shown) to provide a hydraulic fluidsource for operating equipment on the rig. A suitable cab structure M isincluded on the base frame wherein the operator of the drillingapparatus may suitably control the various controls (not shown) whichoperate the motive drill structure, the power supplies and the con trolsfor the motors on the drilling rigs. Included on the base frame arestabilizing support members 16 which are hydraulically operated tosupport the head frame 20 when it is elevated. Journaled on upstandingflange structures 22 of the base frame is the elongated head frame 2 0,the head frame being supported through suitable pivot means 24 and beingelevated between a horizontal and an inclined or vertical positionthrough suitable hydraulic actuators (not shown).

The head frame is comprised of a mast structure including a pair ofguide masts 25, 26 and rear supporting masts 28 which are suitablyinterconnected through cross bracing 30 with a bottom and top supportmember 311, 32, respectively. Positioned between the top and bottomsupport members of the head frame and extending parallel to the guidemasts 25, 26 are a pair of elongated ball screw members or drive screws35, 36 which are suitably journaled in the: bottom and top supports ormembers 31, 32 of the head frame through suitable means to behereinafter identified. The ball screws or lead screws mount a drillhead structure, indi cated generally at 50, which include guide members52 and a drill head frame 54 with the cooperating ball nut structuresindicated at 55, 56 mounted in the drill head frame 54. The drill headframe includes the rotary drill power assembly, indicated generally at60, which mounts in turn the drill rod 62 and the entire assembly isadvanced up and down the head frame being guided thereon by means of theguide members 52 on the drill head frame 54 which bear against the guidemasts 25, 26. The drill power assembly may be mounted on the top orbottom of the drill head frame, as desired. The screw members 35, 36 arerotated, as will be hereinafter identified, and the ball nut structuresinclude conventional balls which ride in the grooves of the screws withrotation of the same to advance the drill head up and down the headframe. At the top of the head frame or bottom, if desired, is mountedthe synchronizing drive assembly for the ball screw members, the driveassembly including gearing heads 72 with an interconnecting shaft 74operating from the drive assembly to insure synchronization of the ballscrew members 35, 36 in the operation of the drill head assembly or themovement of the same. Although not shown, it will be understood that thehydraulic fluid lines extend along the head frame 20 to thesynchronizing screw drive as sembly 70 and through flexible hoses to therotary drill power assembly 60 on the drill head. The drill headassembly 60 and synchronizing drive may be powered hydraulically,electrically or pneumatically, as desired.

The details of the drilling apparatus are shown herein only schematicsince this is one application of the invention which involves themounting of the ball screws or lead screws in an apparatus wherein thescrew members are elongated and subject to loading which could applydistorting forces to the elongated screw members if they were mountedfor compression during loading. Thus, the invention herein relates tothe particular mounting of the screw members and journaling of the same,as will be hereinafter identified, and this principle could be appliedto structures other than drilling apparatus. For this reason, thedrilling apparatus is shown only schematically for the purpose ofexplaining the application of the invention.

In the sectional view of FIG. 3, one of the screw members is showntogether with its mounting on the head frame and the associated drivestructure for the screw member. Thus as will be seen in FIG. 3, thescrew drive motive means is indicated generally at with the drive shaft71 operating through gearing 72 which is mounted on the upper head braceor support 32 of the head frame 20. In the embodiment shown, the screwmember 35 is journaled in the upper end of the head frame through thrustbearings indicated at 75 and included as part of the gearing 72. Aninternal splined drive shaft 78 having an internal splined surface 79 isconnected to the gearing and is coupled to the screw member through acoupling structure indicated generally at 80. This includes a splittransfer thrust collar 82 which fits around a flange extension 84 on thedrive shaft 78. The transfer thrust collar 82 which is formed in twoparts defines an annular shoulder portion 85 which fits around acircular or cylindrical flange portion 88 on one end of the screw member35. Beyond the surface of the cylindrical shoulder or flange 88 is anexternal splined surface 89 which couples the screw member to thesplined surface 79 of the drive shaft for imparting rotative movementthereto. As will be seen in the drawings, longitudinal clearance isprovided between the splined surfaces and the cylindrical flanges 84 and88 to permit axial movement between the drive shaft and the screwmember. The split transfer thrust collar is held in assembledrelationship (see FIG. 4) by means of a circular retaining collar 92which fits around the same, with the retaining collar being held inposition by means of snap rings 94 fitted into grooves in the externalsurface of the thrust collar. In FIG. 3, only the ball nut portion 55 ofthe drill head is shown to indicate the loading on the screw member. Aswill be recognized, the screw member and nut may be of a conventionalconstruction and the application of the same may be other than in adrilling apparatus wherein loading of some part carried by the nut willeffect forces on the screw member as the same is rotated to advance thenut member along the extent of the screw member.

The lower or opposite end of the screw member is journaled in the lowerbrace or support 31 of the head frame 20. This mounting structure isshown generally at and includes a bearing retainer 102 mounted on theopposite shaft extremity of the screw member 35. The bearing retainerincludes a suitable O-ring type seal 103 positioned in the suitablegroove therein and bearing against the cylindrical end of the screwmember which as will be later noted, is preferably tapered toward itsouter extremity and includes a threaded extension 104. The slidingbearing retainer has a cylindrical flange section 105 which bearsagainst the movable race of an annular thrust bearing mounting this endof the screw member in the support 31. A suitable sleeve type bushing orjournal 112 is positioned around the bearing retainer 102 and slidablymounts the same in a cylindrical mounting member 115, the mountingmember having an annular flange portion 118 through which screw membersor bolts 119 extend to bolt the same to the lower support 31. A suitableoil seal 112 and cover plate 123 is positioned around the bearingretainer 102 and fitted into the flange adjacent the sleeve bearing orjournal 112 to seal the same. The fixed race of the thrust bearing 110is also mounted in a shoulder portion of the support 115 such that theraces of the thrust bearings 110 are positioned between the bearingretainer 102 and the support member 115 for journaling the lower end ofthe screw member for rotative movement with the journal member 112permitting axial or longitudinal movement, as will be hereinafter noted.The bearing retainer 102 is forced against the movable race of thethrust bearing 110 by means ofa split taper nut 125 which threads on thetapered threaded extremity 104 of the screw member and preloads or takesup slack in the thrust bearing (see FIGS. 3 and 5). The taper lockcollar 126 is fitted over the split taper nut and suitable bolt members128 are positioned through apertures 129 in the taper collar lock arethreaded into tapped apertures 130 in the bearing retainer to lock thenut in position after taking out slack or preloading of the bearings. Acap is positioned over the open end or recessed end of the supportmember 115 in which the flange portion 105 of the bearing retainer, thethrust bearings and the lock nut are positioned for the purpose ofcovering or enclosing the same to prevent the entrance of dirt thereto.This is secured to the flange portion 118 of the support member bysuitable means such as screws 141. With this mounting of the screwmember 35 at the lower extremity of the same, the thrust bearings gripthe screen member from the side remote from the end of the screw memberand the journal or sleeve bearing 112 allows for movement of the screwmember axially toward the support effectively decreasing any preloadingof the thrust bearings, but limits movement of the screw member in theopposite direction. Thus, the thrust bearings are gripped from the backand the screw member will not be placed in compression in its mountingin the lower support member. The same effect is produced by the couplingmember 80 connecting the drive shaft 78 to the other end of the screwmember 35 since the coupling member will grip the shaft slightly remotefrom the upper end of the screw member but will allow movement of thescrew member toward the drive shaft while preventing movement of thescrew member beyond the engagement of the flange 85 on the screw memberwith the flanges 84 on the drive shaft and the flange portion 85 on thecoupling member.

With this particular mounting of the screw member, operation of the ballnut drive is caused by rotation of the screw member 35 to advance thenut up and down the extent of the screw member. This will effect aloading on the nut and the screw member whenever the nut is connected tosome means providing a reactive force thereto. In the case of the drillstructure as shown in FIGS. 1 and 2, the drilling head in the head frameis advanced downwardly in a conventional drilling operation and upwardlyin a retractive mode of operation to recover drill bits or in a drivingoperation for back reaming to place a load on the individual nuts 55, 56mounted on the screw members 35, 36 and carrying the drilling headassembly. Thus in a conventional drilling operation, as the drill headis moved downwardly and the drill stem is rotated through its drivemotor 60, resistance of the drill rod is supplied back through the drillhead to provide an upward force on the nuts 55, 56. In FIG. 3, thisupward thrust or resistance is applied to the nuts 55, 56 as the screwmembers 35, 36 are rotated by their drive structure in advancing thedrill head downwardly which will cause the screw members to be placed intension due to the action of the bearing mounting 1 .00 of the screwmembers. The opposite end of the screw member will be free to moveaxially through coupling 80 a limited distance toward the upper support32 of the head frame insuring that the same will not be placed incompression. Thus, in extremely long screw members, a constant tensionforce is applied to the screw members and compressive forces areprevented so that the elongated screw members will not be stressed insuch a manner as to provide sidewise displacement or translationaldisplacement of the same. This will provide for improved accuracy andsmoothness in operation of the drive for the drilling head and willeliminate wear on the screw members.

The same effect is produced by upward movement of the drill head on thehead frame whenever the drill bits are retracted or in the case of aback reaming operation. Loading on the nuts 55, 56 supporting thedrilling head on the head frame will be in a downward direction and thelower end of the screw member 35, 36 will be journaled in such a mannerthat the thrust bearing will permit axial movement slightly loweringmounting member 1115 and separating bearing races llllO placing theforce on the screw member in tension. The upper end or driving end ofthe screw member will be re stricted from downward axial movement due tothe connection of the coupling member with the upper end of the screwmember and the drive shaft loading the screw member in tension toprovide the constant tension application of force to the screw memberand preventing any sidewise displacement and wear of the same.

It will be recognized that while the particular disclosure hereinrelates to a ball nut type drive structure and screw member, that thesame application could be made with conventional screws and nuts inother apparatus. Thus, the elongated screw member could be a lead screwor nut in a machine tool with the same forces applied thereto.

In considering this invention it should be remembered that the presentdisclosure is illustrative only and the scope of the invention could bedetermined by the appended claims.

What is claimed is:

l. A screw drive for a member comprising, an elongated screw member, asupport for mounting each end of said screw member, a splined end on oneend of said screw member with motor means connected to the splined endfor rotating said screw member, a nut mounted on the screw member andmounting the load member to be advanced in either direction along theextent of the screw member with rotation of the screw member by saidmotor means, and bearing means mounting said screw member on saidsupport, said bearing means including thrust bearing journaling saidscrew member for rotative movement and means permitting limited axialmovement of said screw member.

2. The screw drive of claim 1 in which the thrust bearing means isfixedly secured to the shaft in such a manner as to permit the end ofthe shaft to which the bearing means is attached to move axially beyondthe same.

3. The screw drive of claim 1 in which the means in cluded with thethrust bearings are sleeve bearings which permit the axial movement.

4. The screw drive of claim 1 in which the thrust bearing on at leastone end of the screw member is an annular roller bearing with a fixedrace attached to the support and secured remote from the end of thescrew member and with a movable race attached to the shaft in a positionnearest the end of the screw member.

5. The screw drive of claim 4 and including a sleeve bearing meansadditionally mounted on the screw member and permitting limited axialmovement of said movable race of the thrust bearing.

6. The screw drive of claim 4 in which the movable race is mounted in asliding bearing retainer fixed on said screw member with radial bearingmeans positioned between the sliding bearing retainer and the supportfor limited axial movement of the screw member relative to the support.

7. The screw drive of claim 6 in which the movable race of the thrustbearing is secured to the screw member by means of a threaded clamp nutbearing against the sliding bearing retainer and threaded on a threadedextremity of the screw member.

8. The screw drive of claim 1 in which the means permitting axialmovement of the screw member is the splined connection at the other endof said screw member coupling the same to the motor means including thethrust bearings for mounting said other end of said screw member.

9. The screw drive of claim 8 and including a thrust transfer collarconnected to the motor and engaging a flange on the extremity of thescrew member with the splined connections between the screw member andthe motor being positioned within the same andallowing for limited axialmovement of the screw member in the direction of the motor.

10. A screw drive for a member comprising, an elongated screw member, asupport for mounting each end of said screw member, a nut mounted on thescrew member and mounting a load member to be advanced in eitherdirection along the extent of the screw member with relative rotationbetween the screw member and the nut, bearing means mounting said screwmem ber in said support, said bearing means including thrust bearingsjournaling the screw member for rotative movement and means permittinglimited axial movement of the screw member, and means providing a relative movement between the screw member and the nut to advance the loadmember in either direction along the extent of the screw member.

11. A screw drive for a member comprising, an elon gated screw member, asupport for mounting each end of said screw member, a nut mounted on thescrew member and mounting a load member to be advanced in eitherdirection along the extent of the screw member with relative rotationbetween the screw member and the nut, bearing means mounting said screwmember in said support, said bearing means being fixedly secured to theshaft in such a manner as to permit the end of the shafts to which thebearing means is attached to move axially beyond the same, and meansproviding a relative movement between the screw member and the nut toadvance the load member in either direction along the extent of thescrew member.

* l "f =l= l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No- 3 792 .619 Dated February 19, 1974 Inventor(s) Robert ECannon and Walter L. Pehoski I V It is certified that error appears inthe above identified patent and that said Letters Patent are herebycorrected as shown below:

Column 3 line 62 delete 112 and insert the following -l22- Signed andsealed this 11th day of June 1971...

(SEAL) Attest:

EDWARD M.FIETCHER,JR. C. MARSHALL 'DANN Attesting Officer Commissionerof Patents USCOMM-DC GUSTO-P09 FORM F'O-IOSO (IO-69) w u. s. sovninmzmmum: orncz: ml 0-3014,

1. A screw drive for a member comprising, an elongated screw member, asupport for mounting each end of said screw member, a splined end on oneend of said screw member with motor means connected to the splined endfor rotating said screw member, a nut mounted on the screw member andmounting the load member to be advanced in either direction along theextent of the screw member with rotation of the screw member by saidmotor means, and bearing means mounting said screw member on saidsupport, said bearing means including thrust bearing journaling saidscrew member for rotative movement and means permitting limited axialmovement of said screw member.
 2. The screw drive of claim 1 in whichthe thrust bearing means is fixedly secured to the shaft in such amanner as to permit the end of the shaft to which the bearing means isattached to move axially beyond the same.
 3. The screw drive of claim 1in which the means included with the thrust bearings are sleeve bearingswhich permit the axial movement.
 4. The screw drive of claim 1 in whichthe thrust bearing on at least one end of the screw member is an annularroller bearing with a fixed race attached to the support and securedremote from the end of the screw member and with a movable race attachedto the shaft in a position nearest the end of the screw member.
 5. Thescrew drive of claim 4 and including a sleeve bearing means additionallymounted on the screw member and permitting limited axial movement ofsaid movable race of the thrust bearing.
 6. The screw drive of claim 4in which the movable race is mounted in a sliding bearing retainer fixedon said screw member with radial bearing means positioned between thesliding bearing retainer and the support for limited axial movement ofthe screw member relative to the support.
 7. The screw drive of claim 6in which the movable race of the thrust bearing is secured to the screwmember by means of a threaded clamp nut bearing against the slidingbearing retainer and threaded on a threaded extremity of the screwmember.
 8. The screw drive of claim 1 in which the means permittingaxial movement of the screw member is the splined connection at theother end of said screw member coupling the same to the motor meansincluding the thrust bearings for mounting said other end of said screwmember.
 9. The screw drive of claim 8 and including a thrust transfercollar connected to the motor and engaging a flange on the extremity ofthe screw member with the splined connections between the screw memberand the motor being positioned within the same and allowing for limitedaxial Movement of the screw member in the direction of the motor.
 10. Ascrew drive for a member comprising, an elongated screw member, asupport for mounting each end of said screw member, a nut mounted on thescrew member and mounting a load member to be advanced in eitherdirection along the extent of the screw member with relative rotationbetween the screw member and the nut, bearing means mounting said screwmember in said support, said bearing means including thrust bearingsjournaling the screw member for rotative movement and means permittinglimited axial movement of the screw member, and means providing arelative movement between the screw member and the nut to advance theload member in either direction along the extent of the screw member.11. A screw drive for a member comprising, an elongated screw member, asupport for mounting each end of said screw member, a nut mounted on thescrew member and mounting a load member to be advanced in eitherdirection along the extent of the screw member with relative rotationbetween the screw member and the nut, bearing means mounting said screwmember in said support, said bearing means being fixedly secured to theshaft in such a manner as to permit the end of the shafts to which thebearing means is attached to move axially beyond the same, and meansproviding a relative movement between the screw member and the nut toadvance the load member in either direction along the extent of thescrew member.